1. Field of the Invention
The present invention refers to a communication system comprising a network and a plurality of user terminals that are coupled to the network via a communication channel using wireless radio frequency transmission and having a downlink channel for transmitting messages in the direction from the network to the user terminals. Further, the invention relates to a network and a user terminal, both for use in said communication system.
2. Description of the Prior Art
Recently, mobile telephone communication networks and systems have become very popular, for example, the telephone network corresponding to the Global Mobile Satellite (GMS) standards. The GMS systems supports the usual mobile telephone communication and, in addition, a number of further services, e.g. the short message service (SMS) cell broadcast and the point to multipoint multicast (PTM-M) service in the general packet radio system.
The PTM-M service is a service in which the message is transmitted to all subscribers currently located within a geographical area. The message contains a group identifier indicating whether the message is of interest to all subscribers or to only a subset of subscribers or user terminals, e.g. certain mobile telephones also called mobile stations belonging to a specific PTM group. The PTM-M service is a connectless unidirectional service, i.e. in the downlink direction from the network to the user terminal, and is a variable bit rate service.
The object of the present invention is the implementation of the PTM-M service in communication systems, e.g. the Universal Mobile Telecommunication System (UMTS), of the latest generation.
The communication system of the invention comprises a network and a plurality of user terminals that are coupled to the network via a communication channel using wireless radio frequency transmission and having a downlink channel for transmitting messages in the direction from the network to the user terminals, wherein the downlink channel comprises:
a paging channel for transmission of paging messages in paging frames for initiating communication with a user terminal allocated to a paging group of a plurality of user terminals, and a paging indicator channel for transmission of a paging indicator belonging to the paging group when there is a paging message for the user terminal belonging to the paging group, wherein the user terminal processes the next paging frame transmitted on the paging channel to determine whether there is a paging message intended for the user terminal when the paging indicator has been transmitted on the paging indicator channel, and
wherein the paging message on the paging channel comprises a point-to-multipoint-multicast (PTM-M) group identifier to identify a PTM-M group.
A considerable advantage of the present invention is the implementation of the PTM-M service in the communication system, for instance, the UMTS without the requirement of additional channels or downlink transport channels. This is achieved by using a paging channel, a paging indicator channel and a downlink transport channel already provided by the communication system. These channels are destinated to implement the PTM-M service in the communication system. Thereby a substantial increase of the system complexity in the e.g. UMTS is avoided when the PTM-M service is implemented.
Preferably, the paging channel itself is used to transport the PTM-M messages, wherein the paging message on the paging channel comprises one or a plurality of PTM-M messages intended for the PTM-M group identified by means of the PTM-M group identifier. The paging channel may be the secondary common control physical channel (S-CCPCH) of the UMTS.
In an alternative embodiment, the downlink channel may comprise in addition a downlink transport channel shared by several user terminals and allocated for transporting PTM-M messages, wherein the user terminal accesses the PTM-M messages of the downlink transport channel when, in the paging channel, the user terminal has detected a PTM-M identifier of a PTM-M group to which the user terminal is allocated.
In an preferred embodiment, the communication system is the UMTS and the downlink transport channel for PTM-M messages is the known forward access channel (FACH) or the downlink shared channel (DSCH) of the UMTS.
The PTM-M identifiers or the plurality of PTM-M identifiers allocated to a user terminal may be stored in a data memory of the user terminal. This allows a quick decision in the user terminal or the mobile telephone whether a detected PTM-M identifier on the paging channel is of interest to the user terminal or not. This helps to save battery power of the mobile phone as the phone is enabled to re-enter quickly into sleep mode or idle mode in which a low power consumption is attained.
In an preferred embodiment, the PTM-M group identifier is the international mobile group identifier used in the general packet radio system (GPRS).
The method of the invention comprises the following steps:
in a paging channel of the downlink channel, transmitting of paging messages in paging frames for initiating communication with a user terminal allocated to a paging group of a plurality of user terminals,
in a paging indicator channel of the downlink channel, transmitting of a paging indicator allocated to the paging group when there is a paging message for the user terminal belonging to the paging group,
processing the next paging frame transmitted on the paging channel by the user terminal to see, whether there is a paging message intended for the user terminal when the paging indicator has been transmitted on the paging indicator channel, and,
in the paging message of the paging channel, transmitting at least one point-to-multipoint-multicast (PTM-M) group identifier to identify a PTM-M group by the network.
Preferably the method of the invention comprises allocating an area to a cell or to a plurality of cells in the network wherein the user terminal is in the area, and providing the paging indicator channel and the paging channel comprising the PTM-M identifier or plurality of PTM-M identifiers to the cell or to the plurality of cells of the area.
The method may comprise, in an area serviced by the network and divided into a plurality of cells, entering one of said cells by the mobile user terminal and registering of the user terminal to be in said cell by the network of the communication system, providing of PTM-M identifiers on a downlink transport channel of the downlink channel, the information indicating the PTM-M groups supported in said cell by the network, reading the PTM-M identifiers on the downlink transport channel by the user terminal, and comparing the PTM-M identifiers read from the downlink transport channel with PTM-M identifiers being stored in a memory of the user terminal and indicating the PTM-M groups to which the user terminal subscribes in order to determine the PTM-M groups serviced in the cell for said user terminal. These steps effectively support sleep-mode operation of the user terminal or mobile phone in connection with the implementation of the PTM-M service, i.e. an effective way for saving power of the mobile phone.
The invention according to yet another aspect also relates to a network. The above preferred embodiments of the communication system also apply to the network.
Furthermore, the invention relates to a user terminal, e.g., a mobile station, especially for use in a communication system. The above preferred embodiments of the communication system also apply to the user terminal.